A key figure in the Iraq-Niger uranium controversy, Joseph Wilson was sent by the CIA to the west African state in 2002 to investigate a report that Iraq was trying to obtain uranium there.

He returned to say it was highly doubtful such a transaction had occurred.

President George W Bush made the Iraq-uranium claim in his January 2003 State of the Union speech. Critics say the Iraq-Niger assertion, which later was found to be based on forged documents, shows the administration tried to hype intelligence to make a case for war.

Wilson, on a panel of speakers at the National Press Club, said there had been several attempts to discredit him, mainly through an article by Chicago columnist Robert Novak.

Afraid to speak

Novak wrote that two senior administration officials said Wilson's wife had suggested sending her husband to Niger to investigate the uranium report. Novak also named Wilson's wife and said she was a CIA expert on weapons of mass destruction.

Wilson would only speak about his wife's job in hypothetical terms without confirming her place of work. But he said if Novak's column were true, then the Bush administration had breached national security by revealing the name.

"Any time that a senior administration official leaks the name of a CIA operative, even one in the weapons of mass destruction business, what that senior administration official is doing is a breach of national security," Wilson said.

"The reason for it was not to smear me or to even smear my wife," Wilson said. "The reason was to intimidate others from coming forward."

He said when intelligence analysts see attempts to discredit him and the controversial suicide of David Kelly, a British weapons expert on Iraq, they will be reluctant to step forward.

Democrats call for enquiry

Kelly became embroiled last month in the biggest political crisis for British Prime Minister Tony Blair's government to date. The BBC used the former UN weapons inspector as its main, anonymous source for an explosive report that the British government had exaggerated the case for war in Iraq.

British officials later suggested Kelly was the source of the story. Kelly was found dead a few days later.

Democrat senators Tom Daschle of South Dakota and Charles Schumer of New York last week called for an investigation into who exposed Wilson's wife.

But White House spokesman Scott McClellan, during a briefing last month, dismissed claims administration officials had revealed a CIA operative's identity.

"That is not the way this president or this White House operates," he said, addressing a question about the Novak article.

"There is absolutely no information that has come to my attention ... that suggests that there is any truth to that suggestion. No one in this White House would have given authority to take such a step."